Support mixed media tweets

[super-cooper]

Is your feature request related to a problem? Please describe.
Twitter recently launched the ability to tweet multiple videos, or a combination of videos and pictures (see here for an example). Right now, Memebot seems to ignore these tweets.

Describe the solution you'd like
Memebot should embed multiple videos if the tweet contains multiple videos, and should react to the post appropriately for the number of media included.

Describe alternatives you've considered
N/A

Additional context
It seems unlikely that this depends on an update from Tweepy. Based on Twitter's API models, media seems sort of "agnostic," but we do make assumptions that tweets can have multiple images but only one video.

It does seem like we should get the reactions for free, since we don't check for what kind of media it is. However, they weren't created when someone posted a tweet with 4 videos. This could have been a coincidence related to intermittent Twitter API failures, which we are aware of. This could be improved by adding retries to API calls.

[super-cooper]

Some additional context worth considering: We ultimately decided not to post all the pictures of a tweet in Discord because it seemed spammy. Do we still think this? Does it make sense to embed videos iff the tweet only includes a single video? What is the best way to go about this? The solution may be easier when Discord allows bots to create custom UI elements.